1. Field of the Invention
The present invention generally relates to the measurement of ultraviolet (UV) radiation and, more particularly, to a UV radiometer that includes a data collection unit at is applied to a high speed web carrying work pieces to measure UV dosage applied to the work pieces in a UV curing system.
2. Background Description
There are many substances, known as monomers, which can be converted to polymers by chemical reactions. In some cases, these reactions are induced by chemical catalysts and initiators. However, polymerization can also be induced by supplying the initiation energy with visible or ultraviolet (UV) light. Such photochemical reactions have practical as well as theoretical advantages. For example, in certain manufacturing processes, a polymer may be used to coat a surface. The photochemically induced polymerization is referred to as "curing".
There are many applications of UV cured polymers wherein the polymer is applied to a surface as, for example, web press applications, bottle printing, container decorating applications, compact disc (CD) and digital video (or versatile) disc (DVD). These applications require a curing station which typically includes a source of high intensity UV light to initiate the photochemical curing polymerization process.
As UV curing has evolved, it has become increasingly important to establish a method of measuring system performance. Degradation of UV lamps, light guides, and reflectors can cause decreases in UV intensity and create curing problems. If the intensity of the UV light falls below a certain level, curing may not be complete resulting in an incomplete polymerization of the coating. Moreover, a visual inspection will not reveal the problem as the surface of the monomer spot may polymerize but the interior volume will not. It has therefore become mandatory in certain applications to periodically measure the UV energy output of the curing system in order to insure that a sufficient UV intensity is being. However, such measurements are typically not conveniently made, or even possible, using current UV intensity measuring instruments in processes which employ a high speed web to carry work pieces through a curing station. In many cases, the curing applications are physically inaccessible. This has made true process control impossible and poses a continuing quality control problem for many applications.